1. Field of the Invention
The present invention relates generally to a diesel engine swirl chamber and more specifically to a swirl chamber which communicates with the main combustion chamber through an improved multiple transfer passage arrangement.
2. Description of the Prior Art
In previously proposed arrangements (such as disclosed in Japanese Utility Model Application Provisional Publication No. 53-47405 and Japanese Patent Application Provision Publication No. 51-105509) an auxiliary transfer passage or throat has been provided in addition to the main passage so as to allow some of the fuel injected into the swirl chamber to be transferred to the main combustion chamber for the purposes of reducing the peak combustion temperatures and thus suppressing the formation of NO.sub.x. However, in a less preferred arrangement wherein the auxiliary throat or transfer passage 1 is, as shown in FIG. 1, disposed directly opposite the fuel injector nozzle 2 and in alignment with the imaginary center line or trajectory "L" along which the fuel is injected, a drawback is encountered in that the inertia of the fuel tends to cause some of the fuel to enter the main combustion chamber 3 in a liquid or non-atomized state wherein it is poorly mixed with air therein and subsequently exposed to a torch flame from the swirl chamber 4 having a relatively low oxygen content. This of course leads to incomplete combustion of the fuel in the main combustion chamber promoting smoke formation.
Further experiments have shown that if the cross-sectional area of the main transfer passage (which is usually larger than that of the auxiliary one) is reduced while maintaining the cross-sectional area of the auxiliary passage constant, the flame from the swirl chamber propagates into the main combustion chamber with an increased velocity and shortens the combustion time in the main combustion chamber. This promotes good combustion and reduces smoke emission enhances NO.sub.x formation. However, on the other hand if the cross-sectional area of the auxiliary passage is increased while that of the main transfer passage is maintained constant, a larger amount of fuel is permitted to reach the main combustion chamber increasing the combustion time and thus suppresses NO.sub.x formation but enhances smoke formation.
Hence, it has hitherto been very difficult to design a multiple transfer passage swirl chamber arrangement which will simultaneously permit the reduction of both smoke and NO.sub.x in view of the conflicting tendencies noted above.